Method of producing paper, paperboard and cardboard

ABSTRACT

Paper, board and cardboard are produced by a process in which a paper stock is drained in the presence of condensates of basic amino acids with sheet formation. In particular, homo- and cocondensates of lysine and the crosslinked condensates obtainable therefrom by reaction with crosslinking agents are used in amounts of from 0.01 to 5% by weight, based on dry paper stock, as a means of increasing the dry and wet strength and the absorptivity of paper, for fixing anionic dyes and interfering substances in the paper, for increasing the drainage rate and the retention as well as the efficiency of synthetic anionic and cationic retention aids in the production of paper, board and cardboard by draining a paper stock with sheet formation.

The present invention relates to a process for the production of paper,board and cardboard by draining a paper stock in the presence ofpolymers.

It is generally known that paper comprises essentially fibers,consisting of wood and/or of cellulose, and, if required, of mineralfillers, in particular calcium carbonate and/or aluminum silicate, andthat the essential papermaking process consists of separating thesefibers and fillers from a dilute aqueous suspension of these substancesby means of one or more movable wires. It is also known that certainchemicals are added to the suspension of fibers and fillers in water,both for improving the separation process and for achieving or improvingcertain properties of the paper. A very current review of the generallyused paper chemicals and their use is to be found, for example, in—PaperChemistry, J. C. Roberts ed., Blackie Academic & Professional, London,Second edition 1996, —and in—Applications of Wet-End Paper Chemistry,C.O. Au and I. Thorn eds., Blackie Academic & Professional, London,1995.

As is evident from the literature cited, many of the paper chemicalsused are cationic water-soluble polymers or, in other words, cationicpolyelectrolytes or polycations having, preferably, an average or highmolar mass. These products are added to the very dilute paper fiberslurry before the paper sheet forms therefrom on the wire. Depending ontheir composition, they result, for example, in more fine materialremaining behind on the wire or in the separation of the water on thewire taking place more rapidly or in certain substances being fixed tothe paper fibers and hence not entering the white water, and, in thecase of the last property, both the cleanliness of the white water andthe effect of the fixed substances, e.g. dyes or sizes, on theproperties of the finished paper may be important. However, polycationsmay also increase the strength of the paper or impart improved residualstrength to the paper in the wet state. However, this wet strength isgenerally obtained by using polycations which additionally carryreactive groups which react with the paper components or with themselveswith network formation and, owing to the resulting covalent bonds, makethe paper more resistant to water.

U.S. Pat. No. 5,556,938 discloses that the thermal polycondensation ofamino acids is carried out in the presence of organic or inorganicacids. For example, aspartic acid, alanine, arginine, glycine, lysineand tryptophan are mentioned as amino acids. The condensates thusobtainable are used, for example, in detergents and cleaning agents, asscale inhibitor, as dispersants for pigments and as dispersants inpapermaking.

U.S. Pat. No. 3,869,342 discloses cationic, heat-curable resins based onpolyamidoamines, which resins can be crosslinked by reaction withepichlorohydrin and can be cured by heating. Resins of this type areused, for example, as wetstrength agents in papermaking.

The polycations used according to the prior art for said purposes arealmost exclusively polymers of synthetic origin, i.e. products based onpetrochemicals. Important exceptions, however, are the cationicstarches, which originate from the reaction of a plant-based rawmaterial with a synthetic cationizing agent. In rare cases, otherpolysaccharides modified with synthetic cationizing agents are also usedin papermaking, for example cationic guar flour. The literature alsodescribes, as the cationic paper assistant, the polysaccharide chitosan,which is obtained by chemical reaction with chitin from crustaceans, butno permanent practical application is known to date.

Regardless of their specific action profiles, products based onvegetable or animal starting materials frequently have the advantage ofbeing more readily biodegradable on reintroduction into the naturalcycle. The use of plant-based raw materials also helps to protect fossilresources and to reduce carbon dioxide emission.

The polycations based on renewable raw materials and suitable to date aspaper chemicals are exclusively polysaccharides having a very narrowaction profile. The principally used cationic starches are employed forincreasing the dry strength of the paper and, to a lesser extent, alsoas retention aids.

It is an object of the present invention to provide further substanceswhich are based on natural raw materials and, for example, fix anionicsubstances in the paper in papermaking and improve the retention offillers.

We have found that this object is achieved, according to the invention,by a process for the production of paper, board and cardboard bydraining a paper stock in the presence of polymers with sheet formation,if the polymers used are crosslinked condensates which are obtainable byreaction of

(i) homocondensates of basic amino acids, condensates of at least twobasic amino acids and/or cocondensates of basic amino acids andcocondensable compounds with

(ii) at least one crosslinking agent having at least two functionalgroups.

Condensates are derived, for example, from homo- or cocondensates oflysine, arginine, ornithine and/or tryptophan. They are obtainable, forexample, by condensing

(a) lysine, arginine, ornithine, tryptophan or mixtures thereof with

(b) at least one compound cocondensable therewith.

The polymers are prepared by condensation of

(a) lysine, arginine, ornithine, tryptophan or mixtures thereof with

(b) at least one compound selected from the group consisting of themonoamines, diamines, triamines, tetraamines, monoaminocarboxylic acids,lactams, aliphatic aminoalcohols, urea, guanidine, melamine, carboxylicacids, carboxylic anhydrides, diketenes, nonproteinogenic amino acids,alcohols, alkoxylated alcohols, alkoxylated amines, amino sugars, sugarsand mixtures thereof.

Of particular industrial interest here are cocondensates which areobtainable by condensation of

(a) lysine and

(b) at least one compound selected from the group consisting of the C₆-to C₁₈-alkylamines, lactams having 5 to 13 carbon atoms in the ring,nonproteinogenic amino acids, monocarboxylic acids, polybasic carboxylicacids, carboxylic anhydrides and diketenes.

The compounds of groups (a) and (b) are used, for example, in a molarratio of from 100:1 to 1:20, preferably from 100:1 to 1:5, in generalfrom 10:1 to 1:2, in the condensation.

Suitable polymers for papermaking are crosslinked condensates of basicamino acids. Such crosslinked condensates are obtainable, for example,by reaction of

(i) homocondensates of basic amino acids and/or condensates of at leasttwo basic amino acids and/or cocondensates of basic amino acids andcocondensable compounds with

(ii) at least one crosslinking agent having at least two functionalgroups.

The basic amino acids lysine, arginine, ornithine and tryptophan whichare suitable in the condensation as compounds of group (a) can be usedin the condensation in the form of the free bases, of the hydrates, ofthe esters with C₁- to C₄-alcohols and of the salts, such as sulfates,hydrochlorides or acetates. Lysine hydrate and aqueous solutions oflysine are preferably used. Lysine may also be used in the form of thecyclic lactam, α-amino-ε-caprolactam. Lysine mono- or dihydrochloridesor mono- or dihydrochlorides of lysine esters can also be used. If thesalts of compounds of group (a) are used, the equivalent amounts ofinorganic bases, e.g. sodium hydroxide solution, potassium hydroxide ormagnesium oxide, are preferably used in the condensation. The alcoholcomponents of mono- and dihydrochlorides of lysine esters are derived,for example, from low-boiling alcohols, e.g. methanol, ethanol,isopropanol or tert-butanol. Preferably, L-lysine dihydrochloride,DL-lysine monohydrochloride and L-lysine monohydrochloride are used inthe condensation.

Examples of cocondensable compounds of group b) are aliphatic orcycloaliphatic amines, preferably methylamine, ethylamine, propylamine,butylamine, pentylamine, hexylamine, heptylamine, octylamine,nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine,stearylamine, palmitylamine, 2-ethylhexylamine, isononylamine,hexamethylenediamine, dimethylamine, diethylamine, dipropylamine,dibutylamine, dihexylamine, ditridecylamine, N-methylbutylamine,N-ethylbutylamine, cyclopentylamine, cyclohexylamine,N-methylcyclohexylamine, N-ethylcyclohexylamine and dicyclohexylamine.

Suitable diamines, triamines and tetraamines are preferablyethylenediamine, propylenediamine, butylenediamine, neopentyldiamine,hexamethylenediamine, octamethylenediamine, imidazole,5-amino-1,3-trimethylcyclohexylmethylamine, diethylenetriamine,dipropylenetriamine and tripropyltetraamine. Further suitable amines are4,4′-methylenebiscyclohexylamine,4,4′-methylenebis-(2-methylcyclohexylamine),4,7-dioxadecyl-1,10-diamine, 4,9-dioxadodecyl-1,12-diamine,4,7,10-trioxatridecyl-1,13-diamine, 2-(ethylamino)ethylamine,3-(methylamino)propylamine, 3-(cyclohexylamino)propylamine,3-(2-aminoethyl)aminopropylamine, 2-(diethylamino)ethylamine,3-(dimethylamino)propylamine, dimethyldipropylenetriamine,4-aminomethyloctane-1,8-diamine, 3-(diethylamino)propylamine,N,N-diethyl-1,4-pentanediamine, diethylenetriamine, dipropylenetriamine,bis(hexamethylene)triamine, aminoethylpiperazine, aminopropylpiperazine,N,N-bis(aminopropyl)methylamine, N,N-bis(aminopropyl)ethylamine,N,N-bis(aminopropyl)hexylamine, N,N-bis(aminopropyl)octylamine,N,N-dimethyldipropylenetriamine, N,N-bis(3-dimethylaminopropyl)amine,N,N′-1,2-ethanediylbis(1,3-propanediamine), N-(hydroxyethyl)piperazine,N-(aminoethyl)piperazine, N-(aminopropyl)piperazine,N-(aminoethyl)morpholine, N-(aminopropyl)morpholine,N-(aminoethyl)imidazole, N-(aminopropyl)imidazole,N-(aminoethyl)hexamethylenediamine, N-(aminopropyl)hexamethylenediamine,N-(aminoethyl)ethylenediamine, N-(aminopropyl)ethylenediamine,N-(aminoethyl)butylenediamine, N-(aminopropyl)butylenediamine,bis(aminoethyl)piperazine, bis(aminopropyl)piperazine,bis(aminoethyl)hexamethylenediamine,bis(aminopropyl)hexamethylenediamine, bis(aminoethyl)ethylenediamine,bis(aminopropyl)ethylenediamine, bis(aminoethyl)butylenediamine,bis(aminopropyl)butylenediamine, and oxypropylamines, preferablyhexyloxyamine, octyloxyamine, decyloxyamine and dodecyloxyamine.

Aliphatic amino alcohols are, for example, 2-aminoethanol,3-amino-1-propanol, 1-amino-2-propanol, 2-(2-aminoethoxy)ethanol,2-[(2-aminoethyl)amino]ethanol, 2-methylaminoethanol,2-(ethylamino)ethanol, 2-butylaminoethanol, diethanolamine,3-[(hydroxyethyl)amino]-1-propanol, diisopropanolamine,bis(hydroxyethyl)aminoethylamine, bis(hydroxypropyl)aminoethylamine,bis(hydroxyethyl)aminopropylamine andbis(hydroxypropyl)aminopropylamine.

Suitable monoaminocarboxylic acids are preferably glycine, alanine,sarcosine, asparagine, glutamine, 6-aminocaproic acid, 4-aminobutyricacid, 11-aminolauric acid and lactams having 5 to 13 carbon atoms in thering, such as caprolactam, laurolactam or butyrolactam. Glucosamine,melamine, urea, guanidine, polyguanidine, piperidine, morpholine,2,6-dimethylmorpholine and tryptamine are also suitable. Particularlypreferably used polymers are those which are obtainable by condensationof

a) lysine with

b) hexamethylenediamine, octylamine, monoethanolamine,octamethylenediamine, diaminododecane, decylamine, dodecylamine,caprolactam, laurolactam, aminocaproic acid, aminolauric acid ormixtures thereof.

Further cocondensable compounds b) are, for example, saturatedmonocarboxylic acids, unsaturated monocarboxylic acids, polybasiccarboxylic acids, carboxylic anhydrides, diketenes,monohydroxycarboxylic acids, monobasic polyhydroxycarboxylic acids andmixtures of said compounds. Examples of saturated monobasic carboxylicacids are formic acid, acetic acid, propionic acid, butyric acid,valeric acid, caproic acid, octanoic acid, nonanoic acid, lauric acid,palmitic acid, stearic acid, arachidic acid, behenic acid, myristicacid, 2-ethylhexanoic acid and all naturally occurring fatty acids andmixtures thereof.

Examples of unsaturated monobasic carboxylic acids are acrylic acid,methacrylic acid, crotonic acid, sorbic acid, oleic acid, linoleic acidand erucic acid. Examples of polybasic carboxylic acids are oxalic acid,fumaric acid, maleic acid, malonic acid, succinic acid, itaconic acid,adipic acid, aconitic acid, azeleic acid, pyridinedicarboxylic acid,furandicarboxylic acid, phthalic acid, terephthalic acid, diglycolicacid, glutaric acid, substituted C₄-dicarboxylic acids, sulfosuccinicacid, C₁- to C₆-alkylsuccinic acids, C₂-C₂₆-alkenylsuccinic acids,1,2,3-propanetricarboxylic acid, 1,1,3,3-propanetetracarboxylic acid,1,1,2,2-ethanetetracarboxylic acid, 1,2,3,4-butanetetracarboxylic acid,1,2,2,3-propanetetracarboxylic acid, 1,3,3,5-pentanetetracarboxylicacid, 1,2,4-benzenetricarboxylic acid and 1,2,4,5-benzenetetracarboxylicacid. Examples of suitable carboxylic anhydrides are mono- anddianhydrides of butanetetracarboxylic acid, phthalic anhydride,acetylcitric anhydride, maleic anhydride, succinic anhydride, itaconicanhydride and aconitic anhydride.

Particularly preferred polymers are those which are obtainable bycondensation of

a) lysine with

b) lauric acid, palmitic acid, stearic acid, succinic acid, adipic acid,ethylhexanoic acid or mixtures thereof.

Other suitable components b) are alkyldiketenes having 1 to 30 carbonatoms in the alkyl group and diketene itself. Examples of alkyldiketenesare methyldiketene, hexyldiketene, cyclohexyldiketene, octyldiketene,decyldiketene, dodecyldiketene, palmityldiketene, stearyldiketene,oleyldiketene, octadecyldiketene, eicosyldiketene, docosyldiketene andbehenyldiketene.

Examples of monohydroxycarboxylic acids are malic acid, citric acid andisocitric acid. Polyhydroxycarboxylic acids are, for example, tartaricacid, gluconic acid, bis(hydroxymethyl)propionic acid and hydroxylatedunsaturated fatty acids, for example dihydroxystearic acid.

Other suitable components b) are nonproteinogenic amino acids, forexample anthranilic acid, N-methylamino-substituted acids, such asN-methylglycine, dimethylaminoacetic acid, ethanolaminoacetic acid,N-carboxymethylaminocarboxylic acid, nitrilotriacetic acid,ethylenediamineacetic acid, ethylenediaminetetraacetic acid,diethylenetriaminepentaacetic acid, hydroxyethylenediaminetriaceticacid, diaminosuccinic acid, and C₄- to C₂₆-aminoalkylcarboxylic acids,for example 4-aminobutyric acid, 6-aminocaproic acid and11-aminoundecanoic acid. The acids can be used in the condensation inthe form of the free acids or in the form of their salts with alkalimetal bases or amines.

Other suitable components b) are alcohols, for example monohydricalcohols having 1 to 22 carbon atoms in the molecule, such as methanol,ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol,n-pentanol, hexanol, 2-ethylhexanol, cyclohexanol, octanol, decanol,dodecanol, palmityl alcohol and stearyl alcohol. Other suitable alcoholsare, for example, ethylene glycol, propylene glycol, glycerol,polyglycerols having 2 to 8 glycerol units, erythritol, pentaerythritoland sorbitol. The alcohols may, if required, be alkoxylated. Examples ofsuch compounds are the adducts of from 1 to 200 mol of a C₂- toC₄-alkylene oxide with one mole of an alcohol. Suitable alkylene oxidesare, for example, ethylene oxide, propylene oxide and butylene oxides.Ethylene oxide or propylene oxide is preferably used or both ethyleneoxide and propylene oxide in the form of blocks are subjected to anaddition reaction with the alcohols, it being possible for first asequence of ethylene oxide units and then a sequence of propylene oxideunits to undergo an addition reaction with the alcohols or firstpropylene oxide and then ethylene oxide to undergo an addition reactionwith the alcohols. Random addition of ethylene oxide and propylene oxideand a different arrangement of the blocks in the alkoxylated productsare also possible. Of particular interest are, for example, the adductsof from 3 to 20 mol of ethylene oxide with one mole of a C₁₃/C₁₅-oxoalcohol or of fatty alcohols. The alcohols can, if required, contain adouble bond, an example being oleyl alcohol. Alkoxylated amines whichare derived, for example, from the abovementioned amines and areobtainable by reacting ethylene oxide and/or propylene oxide canlikewise be used as component (b). Examples are the adducts of from 5 to30 mol of ethylene oxide with 1 mol of stearylamine, oleylamine orpalmitylamine. In addition, suitable components (c) are naturallyoccurring amino sugars, such as chitosan or chitosamine and compoundswhich are obtainable from carbohydrates by reductive amination, forexample aminosorbitol. The condensates can, if required, containcondensed carbohydrates, such as glucose, sucrose, dextrin, starch anddegraded starch, maltose and sugar-carboxylic acids, such as gluconicacid, glutaric acid, glucurolactone and glucuronic acid.

The abovementioned components may be used in the condensation either inthe form of the free bases (such as amines) or in the form of thecorresponding salts, for example the ammonium salts with inorganic ororganic acids. In the case of carboxylic acids, the cocondensablecompounds (b) may be used in the condensation in the form of the freecarboxylic acids or in the form of their alkali metal, alkaline earthmetal or ammonium salts.

The condensation can be carried out in the absence of a solvent, in anorganic solvent or in an aqueous medium. Advantageously, the reactioncan be carried out in an aqueous medium at concentrations of thecompounds of groups (a) and (b) of, for example, from 10 to 98% byweight at from 120 to 300° C. In a particularly preferred embodiment ofthe process for the preparation of such compounds the condensation iscarried out in water at concentrations of components (a) and (b) of from20 to 70% by weight under superatmospheric pressure at from 140 to 250°C. However, the condensation can also be carried out in an organicsolvent, such as dimethylformamide, dimethyl sulfoxide,dimethylacetamide, glycol, polyethylene glycol, propylene glycol,polypropylene glycol, monohydric alcohols, adducts of ethylene oxideand/or propylene oxide with monohydric alcohols, with amines or withcarboxylic acids. If aqueous solutions of the reactants (a) and (b) areused as starting materials, the water can, if required, also bedistilled off before or during the condensation. The condensation can becarried out under atmospheric pressure with removal of water.Preferably, the water formed in the condensation is removed from thereaction mixture. The condensation can be carried out undersuperatmospheric, atmospheric or reduced pressure. The duration of thecondensation is, for example, from 1 minute to 50 hours, preferably from30 minutes to 16 hours. The condensates have, for example, molar massesM_(w) of from 300 to 1,000,000, preferably from 500 to 100, 000.

The condensation can, if required, also be carried out in the presenceof mineral acids as catalysts. The concentration of mineral acids is,for example, from 0.001 to 5, preferably from 0.01 to 1% by weight,based on the basic amino acids. Examples of mineral acids suitable as acatalyst are hypophosphorous acid, hypodiphosphoric acid, phosphorousacid, hydrochloric acid, sulfuric acid or mixtures of said acids. Thealkali metal, ammonium and alkaline earth metal salts of the acids mayalso be used as a catalyst.

Crosslinked condensates of basic amino acids are also suitable aspolymers for papermaking. Such crosslinked condensates are obtainable,for example, by reacting

(i) homocondensates of basic amino acids and/or condensates of at leasttwo basic amino acids and/or cocondensates of basic amino acids andcocondensable compounds with

(ii) at least one crosslinking agent having at least two functionalgroups.

Preferred crosslinking agents (ii) are the following compounds:α,ω-dichloroalkanes or vicinal dichloroalkanes, epihalohydrins,bischlorohydrin ethers of polyols, bischlorohydrin ethers ofpolyalkylene glycols, esters of chloroformic acid, phosgene, diepoxides,polyepoxides, diisocyanates and polyisocyanates.

Halogen-free crosslinking agents are particularly advantageously used.The halogen-free crosslinking agents are at least bifunctional and arepreferably selected from the group consisting of:

(1) ethylene carbonate, propylene carbonate and/or urea,

(2) monoethylenically unsaturated carboxylic acids and their esters,amides and anhydrides, at least dibasic saturated carboxylic acids orpolycarboxylic acids and the esters, amides and anhydrides derivedtherefrom in each case,

(3) reaction products of polyetherdiamines, alkylenediamines,polyalkylenepolyamines, alkylene glycols, polyalkylene glycols ormixtures thereof with monoethylenically unsaturated carboxylic acids,esters, amides or anhydrides of monoethylenically unsaturated carboxylicacids, the reaction products having at least two ethylenicallyunsaturated double bonds or carboxamide, carboxyl or ester groups asfunctional groups,

(4) reaction products of dicarboxylic esters with ethyleneimine, whichreaction products contain at least two aziridino groups,

(5) diepoxides, polyepoxides, diisocyanates and polyisocyanates andmixtures of said crosslinking agents.

Suitable crosslinking agents of group (1) are ethylene carbonate,propylene carbonate and urea. Of this group of monomers, propylenecarbonate is preferably used. The crosslinking agents of this groupreact to give amino-containing urea compounds.

Suitable halogen-free crosslinking agents of group (2) are, for example,monoethylenically unsaturated monocarboxylic acids, such as acrylicacid, methacrylic acid and crotonic acid, and the amides, esters andanhydrides derived therefrom. The esters may be derived from alcohols of1 to 22, preferably 1 to 18, carbon atoms. The amides are preferablyunsubstituted but may carry a C₁- to C₂₂-alkyl radical as a substituent.

Further halogen-free crosslinking agents of group (2) are at leastdibasic saturated carboxylic acids, such as dicarboxylic acids, and thesalts, diesters and diamides derived therefrom. These compounds can becharacterized, for example, with the aid of the formula

where

In addition to the dicarboxylic acids of the formula I, for example,monoethylenically unsaturated dicarboxylic acids, such as maleic acid oritaconic acid, are suitable. The esters of the suitable dicarboxylicacids are preferably derived from alcohols of 1 to 4 carbon atoms.Suitable dicarboxylic esters are, for example, dimethyl oxalate, diethyloxalate, diisopropyl oxalate, dimethyl succinate, diethyl succinate,diisopropyl succinate, di-n-propyl succinate, diisobutyl succinate,dimethyl adipate, diethyl adipate and diisopropyl adipate. Suitableesters of ethylenically unsaturated dicarboxylic acids are, for example,dimethyl maleate, diethyl maleate, diisopropyl maleate, dimethylitaconate and diisopropyl itaconate. Substituted dicarboxylic acids andtheir esters, such as tartaric acid (D- and L-form and racemate) andtartaric esters, such as dimethyl tartrate and diethyl tartrate, arealso suitable.

Suitable dicarboxylic anhydrides are, for example, maleic anhydride,itaconic anhydride and succinic anhydride. The crosslinking ofamino-containing compounds of component (a) with the abovementionedhalogen-free crosslinking agents is carried out with the formation ofamido groups or, in the case of amides such as adipamide, bytransamidation. Maleic esters, monoethylenically unsaturateddicarboxylic acids and their anhydrides can effect crosslinking both byformation of carboxamide groups and by a Michael addition reaction withNH groups of the component to be crosslinked (for example ofpolyamidoamines).

At least dibasic saturated carboxylic acids include, for example, tri-and tetracarboxylic acids, such as citric acid, propanetricarboxylicacid, ethylenediaminetetraacetic acid and butanetetracarboxylic acid.Suitable crosslinking agents of group (2) are furthermore the salts,esters, amides and anhydrides derived from the abovementioned carboxylicacids.

Other suitable crosslinking agents of group (2) are polycarboxylicacids, which are obtainable by polymerizing monoethylenicallyunsaturated carboxylic acids or anhydrides. Examples of suitablemonoethylenically unsaturated carboxylic acids are acrylic acid,methacrylic acid, fumaric acid, maleic acid and/or itaconic acid. Forexample, suitable crosslinking agents are polyacrylic acids, copolymersof acrylic acid and methacrylic acid or copolymers of acrylic acid andmaleic acid.

Further suitable crosslinking agents (2) are prepared, for example, bypolymerizing anhydrides, such as maleic anhydride, in an inert solvent,such as toluene, xylene, ethylbenzene or isopropylbenzene, or solventmixtures in the presence of free radical initiators. The initiators usedare preferably peroxyesters, such as tert-butyl per-2-ethylhexanoate. Inaddition to the homopolymers, copolymers of maleic anhydride aresuitable, for example copolymers of acrylic acid and maleic anhydride orcopolymers of maleic anhydride and a C₂- to C₃₀-olefin.

For example, copolymers of maleic anhydride and isobutene or copolymersof maleic anhydride and diisobutene are preferred. The copolymerscontaining anhydride groups can, if required, be modified by reactionwith C₁- to C₂₀-alcohols or ammonia or amines and can be used in thisform as crosslinking agents.

The molar mass M_(w) of the homo- and copolymers is, for example, up to10,000, preferably from 500 to 5000. Polymers of the abovementioned typeare described, for example, in EP-A-0 276 464, U.S. Pat. No. 3,810,834,GB-A-1 411 063 and U.S. Pat. No. 4,818,795. The at least dibasicsaturated carboxylic acids and the polycarboxylic acids can also be usedas crosslinking agents in the form of the alkali metal or ammoniumsalts. The sodium salts are preferably used. The polycarboxylic acidsmay be neutralized partly, for example up to 10 to 50 mol %, orcompletely.

Preferably used compounds of group (2) are dimethyl tartrate, diethyltartrate, dimethyl adipate, diethyl adipate, dimethyl maleate, diethylmaleate, maleic anhydride, maleic acid, acrylic acid, methyl acrylate,ethyl acrylate, acrylamide and methacrylamide.

Halogen-free crosslinking agents of group (3) are, for example, reactionproducts of polyetherdiamines, alkylenediamines, polyalkylenepolyamines,alkylene glycols, polyalkylene glycols or mixtures thereof with

monoethylenically unsaturated carboxylic acids,

esters of monoethylenically unsaturated carboxylic acids,

amides of monoethylenically unsaturated carboxylic acids or

anhydrides of monoethylenically unsaturated carboxylic acids.

The polyetherdiamines are prepared, for example, by reactingpolyalkylene glycols with ammonia. The polyalkylene glycols may containfrom 2 to 50, preferably from 2 to 40, alkylene oxide units. These maybe, for example, polyethylene glycols, polypropylene glycols,polybutylene glycols or block copolymers of ethylene glycol andpropylene glycol, block copolymers of ethylene glycol and butyleneglycol or block copolymers of ethylene glycol, propylene glycol andbutylene glycol. In addition to the block copolymers, random copolymersof ethylene oxide and propylene oxide and, if required, butylene oxide,are suitable for the preparation of the polyetherdiamines.Polyetherdiamines are furthermore derived from polytetrahydrofuranswhich have from 2 to 75 tetrahydrofuran units. The polytetrahydrofuransare likewise converted into the corresponding α,ω-polyetherdiamines byreaction with ammonia. Polyethylene glycols or block copolymers ofethylene glycol and propylene glycol are preferably used for thepreparation of the polyetherdiamines.

Suitable alkylenediamines are, for example, ethylenediamine,propylenediamine, 1,4-diaminobutane and 1,6-diaminohexane. Suitablepolyalkylenepolyamines are, for example, diethylenetriamine,triethylenetetramine, dipropylenetriamine, tripropylenetetramine,dihexamethylenetriamine, aminopropylethylenediamine,bisaminopropylethylenediamine and polyethyleneimines having molar massesof up to 5000. The amines described above are reacted withmonoethylenically unsaturated carboxylic acids, esters, amides oranhydrides of monoethylenically unsaturated carboxylic acids so that theproducts formed have at least 2 ethylenically unsaturated double bondsor carboxamido, carboxyl or ester groups as functional groups. Thus, forexample in the reaction of the suitable amines or glycols with maleicanhydride, compounds which can be characterized, for example, with theaid of the formula II:

where X, Y and Z are each O or NH

and Y is additionally CH₂,

m, n are each 0-4 and

p and q are each 0-45,000,

are obtained.

The compounds of the formula (II) are obtainable, for example, byreacting alkylene glycols, polyethylene glycols, polyethyleneimines,polypropyleneimines, polytetrahydrofurans, α,ω-diols or α,ω-diamineswith maleic anhydride or with the abovementioned other monoethylenicallyunsaturated carboxylic acids or carboxylic acid derivatives. Thepolyethylene glycols suitable for the preparation of the crosslinkingagents II preferably have molar masses of from 62 to 10,000, the molarmasses of the polyethyleneimines are preferably from 129 to 50,000 andthose of the polypropyleneimines from 171 to 50,000. Suitable alkyleneglycols are, for example, ethylene glycol, 1,2-propylene glycol,1,4-butanediol and 1,6-hexanediol.

Preferably used α,ω-diamines are ethylenediamine, and α,ω-diaminesderived from polyethylene glycols or from polytetrahydrofurans eachhaving molar masses M_(w) of from about 400 to 5000.

Particularly preferred crosslinking agents of the formula II arereaction products of maleic anhydride with α,ω-polyetherdiamines havinga molar mass of from 400 to 5000, the reaction products ofpolyethyleneimines having a molar mass of from 129 to 50,000 with themaleic anhydride and the reaction products of ethylenediamine ortriethylenetetramine with maleic anhydride in the molar ratio of 1: atleast 2. In the reaction of polyalkylene glycols or diols withmonoethylenically unsaturated carboxylic acids or their esters, amidesor anhydrides, crosslinking agents in which the monoethylenicallyunsaturated carboxylic acids or their derivatives are linked via anamido group to the polyetherdiamines, alkylenediamines orpolyalkylenepolyamines and via an ester group to the alkylene glycols orpolyalkylene glycols are formed with retention of the double bond of themonoethylenically unsaturated carboxylic acids or their derivatives.These reaction products contain at least two ethylenically unsaturateddouble bonds. This type of crosslinking agent undergoes a Michaeladdition reaction with the amino groups of the compounds to becrosslinked, said addition reaction taking place at the terminal doublebonds of these crosslinking agents and possibly additionally with theformation of amido groups.

Polyetherdiamines, alkylenediamines and polyalkylenepolyamines canundergo a Michael addition reaction with maleic anhydride or with theethylenically unsaturated carboxylic acids or their derivatives alsowith addition of the double bond. Here, crosslinking agents of theformula III

where X, Y and Z are each O or NH

and Y is additionally CH₂,

R¹ is H or CH₃,

R² is H, COOMe, COOR or CONH₂,

R³ is OR, NH₂, OH or OMe,

R is C₁- to C₂₂-alkyl,

Me is H, Na, K, Mg or Ca,

m and n are each 0-4 and

p and q are each 0-45,000,

are obtained.

Via their terminal carboxyl or ester groups, the crosslinking agents ofthe formula (III) effect crosslinking with the amino-containingcompounds with formation of an amido function. This class of crosslinkersystems includes the reaction products of monoethylenically unsaturatedcarboxylic esters with alkylenediamines and polyalkylenepolyamines; forexample, the adducts of ethylenediamine, diethylenetriamine,triethylenetetramine, tetraethylenepentamine and polyethyleneimineshaving molar masses of, for example, from 129 to 50,000 with acrylic ormethacrylic esters are suitable, at least 2 mol of the acrylic ormethacrylic ester being used per mole of the amine component. The C₁- toC₆-alkyl esters of acrylic acid or methacrylic acid are preferably usedas the esters of monoethylenically unsaturated carboxylic acids. Methylacrylate and ethyl acrylate are particularly preferred for thepreparation of the crosslinking agents. The crosslinking agents whichare prepared by a Michael addition reaction of polyalkylene polyaminesand ethylenically unsaturated carboxylic acids, esters, amides oranhydrides may have more than two functional groups. The number of thesegroups depends on the molar ratio in which the reactants are used in theMichael addition reaction. For example, from 2 to 10, preferably from 2to 8, mol of ethylenically unsaturated carboxylic acids or theirderivatives can be subjected to a Michael addition reaction per mole ofa polyalkylenepolyamine containing 10 nitrogen atoms. From at least 2 tonot more than 4 mol of the ethylenically unsaturated carboxylic acids ortheir derivatives can be subjected to a Michael addition reaction with,in each case, 1 mol of polyalkylenediamines and alkylenediamines.

When diethylenetriamine and a compound of the formula

where X is OH, NH₂ or OR¹ and R¹ is C₁- to C₂₂-alkyl, are subjected to aMichael addition reaction, for example, a crosslinking agent of thestructure

where X is NH₂, OH or OR¹ and

R¹ is C₁- to C₂₂-alkyl,

is formed.

The secondary NH groups in the compounds of the formula IV can, ifrequired, undergo a Michael addition reaction with acrylic acid,acrylamide or acrylic esters.

The compounds of the formula II which contain at least 2 carboxyl groupsand are obtainable by reacting polyetherdiamines, ethylenediamine orpolyalkylenepolyamines with maleic anhydride, or Michael adductscontaining at least two ester groups and obtained frompolyetherdiamines, polyalkylenepolyamines or ethylenediamine and estersof acrylic acid or methacrylic acid with in each case monohydricalcohols of 1 to 4 carbon atoms, are preferably used as crosslinkingagents of group (3).

Suitable halogen-free crosslinking agents of group (4) are reactionproducts which are prepared by reacting dicarboxylic esters, which havebeen completely esterified with monohydric alcohols of 1 to 5 carbonatoms, with ethyleneimine. Examples of suitable dicarboxylic esters aredimethyl oxalate, diethyl oxalate, dimethyl succinate, diethylsuccinate, dimethyl adipate, diethyl adipate and dimethyl glutarate.Thus, bis[β-(1-aziridino)ethyl]oxalamide is obtained, for example, inthe reaction of diethyl oxalate with ethyleneimine. The dicarboxylicesters are reacted with ethyleneimine, for example in a molar ratio of 1to at least 4. Reactive groups of these crosslinking agents are theterminal aziridino groups. These crosslinking agents can becharacterized, for example, with the aid of the formula V:

where n is from 0 to 22.

The crosslinking agents described above can be used either alone or as amixture in the reaction with the abovementioned water-solublecondensates of basic amino acids. The crosslinking reaction is in allcases only continued as long as the resulting products are stillwater-soluble; for example, at least 10 g of the crosslinked polymershould dissolve in 1 l of water at 20° C.

The condensates of the basic amino acids are reacted with at leastbifunctional crosslinking agents, preferably in an aqueous solution orin water-soluble organic solvents. Suitable water-soluble organicsolvents are, for example, alcohols, such as methanol, ethanol,isopropanol, n-propanol and butanols, glycols, such as ethylene glycol,propylene glycol or butylene glycol, or polyalkylene glycols, such asdiethylene glycol, triethylene glycol, tetraethylene glycol anddipropylene glycol, and tetrahydrofuran. The concentration of thestarting materials in the solvents is chosen in each case so that theresulting reaction solutions contain, for example, from 5 to 50% byweight of crosslinked reaction products. Preferably, the crosslinking iscarried out in aqueous solution. The temperatures during the reactionare from 20 to 180° C., preferably from 40 to 95° C. If the reactiontemperature is to be above the boiling point of the solvent used in eachcase, the reaction is carried out under superatmospheric pressure.

These homopolymers and copolymers based on lysine, which may also bereferred to as 2,6-diaminohexanoic acid or 2,6-diaminocaproic acid,differ from most conventional process chemicals for papermaking not onlyin that they are derived from a natural product. After addition to thepaper stock, they also have a plurality of different effects and thusdiffer from the conventional process chemicals and also from those basedon the natural product starch. The polymers to be used according to theinvention strengthen the paper in the dry as well as the wet state, theyincrease the retention of the fillers and of the crill, they acceleratethe drainage of the paper stock on the wire of the paper machine, theyincrease the efficiency of anionic retention aids, they help anionicretention aids to achieve a substantial drainage effect, they improvethe fixation of anionic paper dyes, and they are capable of fixingundesired anionic oligomers and polymers, which are usually interferingsubstances, to the paper fibers and hence of removing them from thecirculation water of the paper machine. They also increase theabsorptivity of the paper.

What is certainly most surprising is that the polymers based on lysinesubstantially increase the wet strength of the paper. Depending on thepapermaking conditions, their wet strength activity is close to oridentical to that of the commercial wet strength chemicals, which arereactive synthetic resins from the aminoplast series or resins based onepichlorohydrin, i.e. polyamidopolyamine/epichlorohydrin resins,referred to below as epichlorohydrin resins for short. For ecologicaland toxicological reasons, there is now a tendency to avoid the use ofboth resin types because the aminoplasts liberate formaldehyde duringand after the processing and moreover display their effect only at lowpH in the paper stock, and because, when epichlorohydrin resins areused, it is not possible to avoid organically bound chlorine in thewaste water of the paper mill and in the paper produced. The immissionof organically bound chlorine, known and measured as “adsorbable organichalogen” (AOX), into the environment should as far as possible beavoided. Both resin types have wet strength activity by virtue of thefact that they react with themselves or with functional groups of thepaper fibers and build up a water-resistant network. Their reactivity isalso evident from their limited shelf life. The polymers based on lysineare not reactive and to date it has not been possible to explain theirwet strength activity on paper.

Wet strength of paper is desired if the paper comes into contact withwater unintentionally or contrary to its intended use and should notdissolve or, after drying, should exhibit its original properties again.In such cases, the paper may additionally or alternatively be sized,i.e. rendered partially hydrophobic with a paper chemical, and hence thepenetration of water into the fiber structure is slowed down. However,there are many paper grades in which very rapid penetration of water isdesirable, it being necessary for the fiber structure to be retained.Examples of such papers are paper hand towels, hygiene papers, paperhandkerchiefs, paper napkins, lavatory paper and filter paper. It hassurprisingly been found that paper to which wet strength has beenimparted by means of polymers based on lysine has very high absorptivitywhich is higher than that which is obtained with the use of commercialwet strength agents, and also higher than that of paper free of wetstrength agents otherwise containing the same raw materials. It is truethat those skilled in the art are familiar with methods for increasingthe absorptivity of paper, for example by impregnating or spraying thepaper web with wetting agents or hydrophilic substances, e.g.polyglycols. However, these known methods reduce the strength of thepaper in the dry state. In the novel process, however, the polymericderivatives of the natural product lysine increase the absorptivity ofthe paper while at the same time increasing the dry strength.

For many applications, the strength possessed by the paper by virtue ofits fiber composition, its filler content and its production process isnot sufficient. This is particularly striking in connection with thegrowing environmental consciousness and the consequently increasing useof waste paper, which has a much lower potential strength than freshpaper fibers. However, even when fresh fibers are used, the naturalstrength is frequently insufficient, particularly if the paper is tocontain a large amount of filler. In such cases, the papermaker attemptsto increase the strength of its product by adding specific chemicals.For this purpose, the paper's surface is generally treated with suitablechemicals, preferably with degraded starch, after the actualpapermaking. If it is intended to use the strength-imparting starch inthe aqueous paper stock, said starch must be reacted with otherchemicals in a special chemical process and thus provided with cationiccharges. It has surprisingly been found that, also by adding polymersbased on the natural product lysine to the aqueous paper stock,according to the novel process, a substantially higher strength can beimparted to the dry paper compared with the paper withoutstrength-imparting chemicals. When used in the stock, they are entirelyequivalent therein to the cationic starches but, in contrast to thelatter, have a number of further advantages, as described further aboveand further below.

Many paper grades are colored by adding specific dyes to the aqueouspaper stock suspension. It is important that the dyes are absorbed asfar as possible completely by the fibers and fillers and do not enterthe waste water. This is a problem particularly when particularlypopular anionic dyes are employed for coloristic and fastness-relevantreasons. If the waste water is excessively polluted in the case ofintensive coloring or if high fastness to bleeding is required, thepapermaker attempts to bind such dyes to the fibers and fillers by meansof fixing agents, it being necessary to ensure that the hue and thepurity of the coloring are not adversely affected by the fixing agent,which nevertheless is very frequently the case. A further problem is thefixing of pigments which are required for the grades which areparticularly lightfast and fast to bleeding. Unless aluminum sulfate canbe used as the fixing agent, as in traditional papermaking in an acidicmedium, these pigments have virtually no intrinsic affinity. It has nowsurprisingly been found that polycations based on lysine are alsocapable of binding anionic dyes and pigments to the paper fibers andensuring substantially colorless waste water, there being no or scarcelyany impairment of the coloristic properties of the colored paper.

It is part of the general prior art to add retention aids and drainageaids to the paper stock prior to sheet formation. These are frequentlyvery high molecular weight cationic polymers. The use of high molecularweight anionic polyacrylamides, which have specific ecologicaladvantages, for this purpose is associated, in the case of neutral andalkaline paper stocks, as increasingly used in practice, with thesimultaneous use of cationic fixing agents because otherwise the optimumretention effect of the anionic polyacrylamides is not obtained and thedrainage of the paper stock may even deteriorate. Polycations based onlysine condensates are capable of optimizing the effect of highmolecular weight anionic polyacrylamides with respect to retention anddrainage. They not only improve the retention effect of these anionicpolymers but also alter the efficiency of the anionic polyacrylamides,resulting in an improvement in the drainage. They are thus superior tocommercial fixing agents in both effects. It is noteworthy that thepolycations based on lysine condensates also improve the efficiency ofhigh molecular weight cationic polyacrylamides as usually used inpapermaking. In addition, they also act by themselves as retention aidsand drainage aids, higher molecular weight polycondensates having betterefficiency than low molecular weight ones.

It is known that anionic oligomers and polymers which aredisadvantageous in papermaking and are therefore referred to asinterfering substances accumulate in the circulation water of a papermachine. Such interfering substances impair, for example, the efficiencyof cationic retention aids and other polycations by neutralizing theirpositive charge and thus rendering them ineffective. It has now beenfound that the polycations based on lysine are also capable of fixing onthe paper fibers those anionic oligomers and polymers which occur asinterfering substances, and hence rendering them harmless and removingthem from the water system of the paper mill.

Those amounts of polymers based on lysine condensates which are requiredfor the effects described vary within wide limits depending on thedesired effect but do not differ fundamentally from the amounts of thecommercial paper chemicals used for a specific effect in each case. Toobtain wet strength, 0.1-5%, preferably 0.5-2, % by weight, based on drypaper stock, of polymers based on lysine should be used. To increase thedry strength of the paper, for example, 0.2-2% by weight, based on drypaper stock, of the lysine polymers are required. For fixing, retentionand drainage effects, for example, 0.01-1, preferably 0.02-0.2, % byweight of polylysine derivatives is used, it also being possible toincrease the required amounts to 2%, based in each case on dry paperstock, for fixing dyes.

In the examples which follow, percentages are by weight, unlessotherwise evident from the context. The K values were determinedaccording to H. Fikentscher, Cellulose-Chemie 13 (1932), 58-64 and71-74, in aqueous solution at 25° C. and a concentration of 0.5% byweight.

Lysine Polycondensate A:

Condensate of lysine and aminocaproic acid in a molar ratio of 1:1,crosslinked with 30% by weight of a bisglycidyl ether of a polyethyleneglycol with 14 ethylene oxide units. Aqueous solution, brought to pH 7.0with hydrochloric acid. The K value of the polycondensate is 64.5 andthe molecular weight M_(w) is 960,000.

Lysine Polycondensate B:

Condensate of lysine, crosslinked with 30% by weight of a bisglycidylether of a polyethylene glycol with 14 ethylene oxide units. Aqueoussolution, brought to pH 7.0 with hydrochloric acid. The K value of thepolycondensate is 52.2.

Lysine Polycondensate G:

Condensate of lysine, crosslinked with 27% by weight of a bisglycidylether of a polyethylene glycol with 14 ethylene oxide units. Aqueoussolution, brought to pH 7.0 with HCl. The K value of the polycondensateis 69.

Lysine Polycondensate H:

Condensate of lysine and ε-caprolactam in the molar ratio of 1:1,crosslinked with 30% by weight of a bisglycidyl ether of a polyethyleneglycol with 14 ethylene oxide units. Aqueous solution, brought to pH 7.0with HCl. The K value of the polycondensate is 51.0.

Comparative Products:

Comparative product I: commercial polyamidopolyamine/ epichlorohydrinresin having a solids content of 13.5% (Luresin ® KNU from BASFAktiengesellschaft) Comparative product II: commercialpolydiallyldimethylammonium chloride having a solids content of 30%(Catiofast ® CS from BASF Aktiengesellschaft) Comparative product III:commercial dicyandiamide resin having a solids content of 45%(Catiofast ® FP from BASF Aktiengesellschaft) Colorant a: commercialdirect dye (C.I. Direct Blue 199) from BASF Aktiengesellschaft:Fastusol ® Blue 75 L Colorant b: commercial pigment preparation (C.I.Pigment Blue 15.1) from BASF Aktiengesellschaft: Fastusol ® P Blue 58 LCationic starch I: cationic potato starch having a degree ofsubstitution of about 0.03 (Hi-Cat 110 from Roquette) Cationic starchII: cationic potato starch having a degree of substitution of about 0.06(Hi-Cat 160 from Roquette)

EXAMPLE 1

In each case the amount, indicated in Table 1, of lysine polycondensateA or of comparative product I is added to a paper stock of unbleachedpine sulfate pulp having a freeness of 25° SR and is allowed to act for1 minute while stirring. 4 sheets having a sheet weight of about 80 g/m²are then formed for each added amount with the aid of a Rapid-Köthensheet former. For comparison, paper sheets having a sheet weight of 80g/m² are then additionally produced from the paper stock described, inthe absence of condensates or conventional paper assistants. Afterdrying by means of a laboratory drying cylinder, the wet breaking lengthaccording to DIN 53112-2 and the capillary rise according to ISO 8787are determined. The test results are shown in Table 1. They show thatthe wet strength achieved using the polymers based on lysine is similarto that achieved using the products of the prior art. The absorptivityof the paper increases with increasing amount of lysine polycondensatebut decreases with increasing amount of epichlorohydrin resin.

TABLE 1 Drying at 90° C. for 10 min; additionally aged for 5 min at 130°C. without Lysine wet strength polycon- Comparative agent densate Aproduct I Addition (% of active 0 0.5 1 0.5 1 ingredient, based on drypaper stock) Basis weight (g/m²) 80.8 81.1 81.0 80.1 80.1 Drying at 90°C. Wet breaking length (m) 173 645 877 577 841 Drying at 130° C. Wetbreaking length (m) 172 655 885 670 855 Capillary rise 10 min (mm) 48 5965 59 48

EXAMPLE 2

In each case the amount of lysine polycondensate A or B shown in Table 2is added to a paper stock of 50 parts of bleached beech sulfite pulp and50 parts of bleached spruce sulfite pulp having a freeness of 31° SR. 3sheets having a sheet weight of about 80 g/m² are then formed for eachadded amount with the aid of the Rapid-Köthen sheet former. After dryingby means of a laboratory drying cylinder, in each case the strengths andthe capillary rise are determined. For comparison, paper sheets having asheet weight of 80 g/m² are additionally produced from said paper stockin the absence of condensates.

The test results are show n in Table 2. They show that, when polymersbased on lysine are used in papermaking, the absorptivity of the paperincreases. The paper strength does not decrease but even increases. Thepolymers based on lysine thus also act as dry strength agents.

TABLE 2 Lysine Lysine without polycondensate B polycondensate A Addition(% of 0.5 1 0.5 1 active ingredient, based on dry pulp) Basis weightg/m² 83.6 83.4 81.8 83.1 83.3 Dry breaking m 2916 3168 3455 3214 3329length Wet breaking m 114 408 570 453 568 length relative wet % 4% 13%16% 14% 17% strength Capillary rise 10 mm 53 62 65 64 66 min

EXAMPLE 3

The amount of the lysine polycondensates and, for comparison, of the twocationic starches stated in each case in Table 3 is added to a paperstock of 60 parts of bleached pine sulfate pulp and 40 parts of bleachedbirch sulfate pulp having a freeness of 25° SR. 2 sheets having a sheetweight of about 80 g/m² are then formed for each added amount with theaid of the Rapid-Köthen sheet former. For comparison, sheets having abasis weight of 80 g/m² are additionally produced from said paper stockin the absence of further additives. After drying by means of alaboratory drying cylinder, the dry breaking length and the wet breakinglength are determined in each case.

The test results are shown in Table 3. They show that the dry paperstrength obtained using the polymers based on lysine in papermaking isthe same as that obtained using cationic starches. In contrast to thecationic starches, an increase in the wet strength of the paper isadditionally obtained with the polylysine derivatives.

TABLE 3 Lysine Cationic starch polycondensate without I II G B Addedamount (% of 1 1 1 1 active ingredient, based on dry paper stock) Drybreaking length (m) 3246 3544 3447 3541 3459 Wet breaking length (m)109.3 106.8 108.8 444.3 390.4 relative wet strength (%) 3.4 3.0 3.2 12.511.3

EXAMPLE 4

In each case the amounts of fixing compositions or polycondensates oflysine stated in Table 4 are added to one liter of a paper stock beatento a freeness of 35° SR, having a consistency of 0.6%, comprising 60parts of bleached birch sulfate pulp and 40 parts of bleached pinesulfate pulp and containing 40 parts of calcium carbonate. The statedamount of a commercial high molecular weight anionic polyacrylamide(Polymin® AE 75 from BASF Aktiengesellschaft) is then added. The paperstock is then drained in a Schopper-Riegler freeness tester, the time inwhich 600 ml of water flows through the wire of the apparatus beingmeasured. The shorter the time, the greater the drainage effect of thecombination of chemicals. The white water which has passed through issubjected to a turbidity measurement. The clearer the white water, thegreater the retaining effect of the combination of chemicals. Forcomparison, a paper sheet which was produced without condensate but inthe presence of anionic polyacrylamide is also tested. The test resultsare shown in Table 4.

They show that, by using lysine polycondensates in papermaking, theretention efficiency of high molecular weight anionic polyacrylamidescan be substantially increased, and to a greater extent than withcommercial fixing compositions. The results also show that the lysinepolycondensates on which the novel process is based impart to theanionic polyacrylamide greater drainage efficiency than the commercialcomparative products.

TABLE 4 Comparative Lysine product polycondensate II III B A Addition offixing composition, % 0 0 0.1 0.1 0.1 0.1 based on dry paper stockanionic PAM % 0.02 0.02 0.02 0.02 0.02 Drainage time for 600 ml sec. 4047 37 47 31 33 Turbidity measured at 588 nm 0.976 0.327 0.142 0.1840.086 0.096

EXAMPLE 5

The procedure is as described in Example 4, except that the polylysinederivatives are compared with two commercial cationic starches. The testresults are shown in Table 5. They show that the lysine polycondensatesin combination with an anionic polyacrylamide substantially acceleratethe drainage of a wood-free paper stock, whereas combinations ofcationic starches and anionic polyacrylamide do not do so. Furthermore,it can be seen that said combinations with lysine polycondensates have abetter retention effect than combinations with cationic starches.

TABLE 5 Lysine polycondensate Cationic starch G G H H I I II II Additionof fixing composition, % 0.1 0.2 0.1 0.2 0.1 0.2 0.1 0.2 based on drypaper stock anionic polyacrylamide % — 0.006 0.006 0.006 0.006 0.0060.006 0.006 0.006 Drainage time for 600 ml sec. 31 20 20 24 21 33 33 3230 Turbidity measured at 588 nm 3.040 0.115 0.108 0.155 0.126 0.4500.438 0.331 0.260

EXAMPLE 6

The procedure is as in Example 4, except that TMP (thermomechanicalpulp) is used as fiber and kaolin (China clay) as filler and a highmolecular weight cationic polyacrylamide (Polymin® KE 78 from BASFAktiengesellschaft) as a retention aid. The test results are shown inTable 6. They show that, by using lysine polycondensates in papermaking,the drainage and retention efficiency of high molecular weight cationicpolyacrylamides can be substantially increased, and to a greater extentthan with commercial fixing compositions.

TABLE 6 Comparative Lysine product polycondensate II III B A Addition offixing composition %¹⁾ 0 0 0.1 0.1 0.1 0.1 cationic PAM %¹⁾ 0.02 0.020.02 0.02 0.02 Drainage time for 600 ml sec. 70 60 30 55 25 25 Turbiditymeasured at 588 nm 0.367 0.247 0.095 0.188 0.076 0.076 ¹⁾based in eachcase on dry paper stock

EXAMPLE 7

The procedure is as in Example 4, except that the comparative productsused are the two cationic starches I and II. The test results are shownin Table 7. They show that, by using lysine polycondensates inpapermaking, the drainage and retention efficiency of high molecularweight cationic polyacrylamides can be substantially increased, and to agreater extent than with commercial cation starches.

TABLE 7 Lysine polycondensate Cationic starch G G H H I I II IIAdditional fixing composition %¹⁾ 0.1 0.2 0.1 0.2 0.1 0.2 0.1 0.2Cationic PAM %¹⁾ — 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004Drainage time for 600 ml sec. 55 32 15 13 16 14 25 24 23 23 Turbiditymeasured at 588 nm 1.195 0.554 0.207 0.163 0.242 0.225 0.498 0.479 0.4030.385 ¹⁾based in each case on dry paper stock

EXAMPLE 8

The procedure is as described in Example 4, except that, instead of highmolecular weight cationic polyacrylamide as a retention aid, onlyvarious amounts of lysine polycondensates are used. The test results areshown in Table 8. They show that lysine polycondensates have apronounced drainage and retention efficiency in papermaking, even whenused alone.

TABLE 8 Stock model: 100 parts of TMP, beaten to 65°SR + 20 parts ofChina clay X1 Consistency: 6 g/l Lysine polycondensate without B AAddition, based % 0 0.05 0.2 0.05 0.2 on dry paper stock Drainage timefor sec. 70 41 25 39 21 600 ml Turbidity 0.367 0.131 0.079 0.130 0.068measured at 588 nm

EXAMPLE 9

The procedure is as described in Example 4, except that cationicstarches are also tested as comparative products. The test results areshown in Table 9. They show that, even when used alone in papermaking,lysine polycondensates have a substantially better drainage andretention efficiency than cationic starches.

TABLE 9 Lysine polycondensate Cationic starch G G H H I I II II Additionof retention aid, % 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 based on dry paperstock Drainage time for 600 ml sec. 55 15 13 19 15 50 48 44 38 Turbiditymeasured at 588 nm 1.195 0.298 0.261 0.410 0.330 1.149 1.037 0.961 0.837

EXAMPLE 10

The amounts of sodium ligninsulfonate, cationic polyacrylamide (Polymin®KE 78 from BASF Aktiengesellschaft) and lysine polycondensates stated inTable 10 are added to one liter of a paper stock having a consistency of0.6% and comprising 50 parts of daily newspapers, 50 parts of linerwastes and 40 parts of kaolin. The paper stock is then drained in aSchopper-Riegler freeness tester for each combination of the statedproducts, the time in which 500 ml of water flow through the wire of theapparatus being measured. The shorter the time, the greater the drainageeffect of the combination of chemicals. The results of the measurementsare shown in Table 10.

They show first of all (experiments nos. 1-6) the known effect wherebythe essentially good drainage effect of the cationic polyacrylamide islost through the addition of the interfering substance sodiumligninsulfonate, even if larger amounts of the drainage aid are used.However, if the interfering substance is bound by addition of thepolylysine derivatives (experiments nos. 8-11 and 13-16), the cationicpolyacrylamide can display its activity again. In the presence of theinterfering substance sodium ligninsulfonate, the polylysines alone(experiments 7 and 12) exhibit scarcely any drainage-acceleratingeffect, even when used in large amounts. The polylysine derivatives cantherefore be used for overcoming the effect of interfering substances.

TABLE 10 Experiment no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Lysincpolycondensate A (5) Lysine polycondensat G (5) 0.16 0.04 0.08 0.12 0.160.16 0.04 0.08 0.12 0.16 Sodium ligninsulfonate % — — 0.25 0.25 0.250.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Cationicpolyacrylamide % — 0.01 — 0.01 0.02 0.04 — 0.04 0.04 0.04 0.04 — 0.040.04 0.04 0.04 Drainage time sec/500 ml 95 81 94 86 86 83 85 78 73 66 6283 79 71 64 56

We claim:
 1. A process for the production of paper, board or cardboard,said process comprising draining a paper stock in the presence of atleast one polymer to form a sheet, wherein said at least one polymer isa crosslinked condensate obtained by reaction of (i) a homocondensate ofat least one basic amino acid, a condensate of at least two basic aminoacids and/or a condensate of at least one basic amino acid and acocondensable compound, with (ii) at least one crosslinking agent havingat least two functional groups, wherein said at least one basic aminoacid, or one of said at least two basic amino acids, is selected fromthe group consisting of lysine, arginine, ornithine, tryptophan andmixtures thereof.
 2. The process as claimed in claim 1, wherein saidcrosslinking agent (ii) is selected from the group consisting ofα,ω-dichloroalkanes, vicinal dichloroalkanes, epihalohydrins,bischlorohydrin ethers of polyols, bischlorohydrin ethers ofpolyalkylene glycols, esters of chloroformic acid, phosgene, diepoxides,polyepoxides, diisocyanates and polyisocyanates.
 3. The process asclaimed in claim 1, wherein the condensates are present in amounts offrom 0.01 to 5% by weight, based on dry paper stock.
 4. The process asclaimed in claim 1, wherein the condensates are present in amounts offrom 0.02 to 2% by weight, based on dry paper stock, for increasing thedry strength of the paper, for increasing the absorptivity of the paperand for fixing anionic dyes in the paper.
 5. The process as claimed inclaim 1, wherein the condensates are present in amounts of from 0.02 to0.2% by weight for fixing interfering substances, for increasing thedrainage rate of the paper stock and for increasing the retention ofcrill and of fillers in papermaking.
 6. The process as claimed in claim1, further comprising adding a synthetic anionic retention aid, whereinthe condensates are present in amounts of from 0.02 to 0.2% by weight,based on dry paper stock, for increasing the drainage effect and theretention effect of the synthetic anionic retention aids.
 7. The processas claimed in claim 1, further comprising adding a synthetic cationicretention aid, wherein the condensates are present in amounts of from0.02 to 0.2% by weight, based on dry paper stock for increasing thedrainage effect and retention effect of the synthetic cationic retentionaids.
 8. The process as claimed in claim 1, wherein the at least onebasic amino acid, or the one of the at least two basic amino acids, islysine.